The present invention relates to an apparatus and technique for generating millimeter and submillimeter radiation and more particularly to an improved technique for providing high power far infrared electromagnetic radiation by coherent stimulated scattering of microwave radiation from an intense relativistic electron beam.
With the advent of laser technology, new areas were developed to provide optical techniques for generating radiation having wide applications to material analysis and communications. This expanding field of laser technology provided new sources of radiation of higher efficiency than prior sources as well as radiation at wavelengths previously unattainable. While such sources greatly expanded the practically attainable wavelengths of the electromagnetic spectrum, generation of radiation in the far infrared region of the optical spectrum in the range of 50 micrometer to 1 millimeter wavelengths still remains relatively unexplored.
Various techniques have been proposed for generating radiation in the millimeter and submillimeter regions including miniaturized microwave tube sources, quantum mechanical sources, and stimulated scattering from relativistic electron beams as exampled by U.S. Pat. No. 3,639,774. In U.S. Pat. No. 3,639,774 far infrared radiation is generated by backscattering microwaves from a relativistic electron beam having a direction along a parallel magnetic field of a magnitude chosen to make the electron cyclotron frequency approximately equal to the microwave frequency. Coherent radiation at far infrared wavelengths is then produced by resonating the backscattered radiation to produce stimulated emission of the far infrared radiation.
While such prior known techniques have had some success in generating far infrared radiation, the available power and tunability of such sources limit their potential application and effective use. In particular, the backscattering techniques have utilized relativistic electron beams having currents on the order of milliamps produced from thermionic emitting cathodes or similar structures producing low power output and narrowband radiation. It has been found that when using low current relativistic electron beams and a microwave frequency approximately equal to the electron cyclotron frequency, the low power output radiation is produced as a result of incoherent backscattering from individual electrons of the beam. It has also been found, that if the microwave frequency iis maintained equal to the cyclotron frequency as current are increased, the microwave source will be depleted via heating of the electrons rather than producing an increase in radiation power output.
While still other techniques have been proposed to generate far infrared radiation using scattering from an electron beam, each is generally restricted to low power outputs or is limited in tunability by the specific structure utilized.
Accordingly, the present invention has been developed to overcome the specific shortcomings of the above known and similar techniques and to provide an improved apparatus and technique for generating tunable high power millimeter and submillimeter radiation.